A hypotensive agent with .alpha..sub.1 -blocking activity is known, for example, 1-(4-amino-6,7-dimethoxy-2-quinazolinyl)-4-(2-furanylcarbonyl)piperazine, generally called prazosin (see U.S. Pat. No. 3,511,836).
Since, however, medicine is a foreign substance to a living body, the dose thereof is preferably as small as possible, so that development of a new medicine which can exhibit a stronger activity has been desired.